High voltage switch assemblies with sub-atmospheric or vacuum type circuit interrupters for electric power circuits and systems are well known in the art. Several examples are shown in U.S. Pat. Nos. 4,568,804; 3,955,167; and 3,471,669. Encapsulated vacuum type switches or circuit breakers are also known and are shown in U.S. Pat. Nos. 3,812,314 and 2,870,298.
In prior art switch assemblies and circuit breakers, a pair of co-acting contacts, one fixed and the other movable, are provided for controlling and interrupting current flow. The contacts are housed in a controlled atmosphere contact assembly, which includes a relatively fragile glass or ceramic housing that is commonly referred to as a “bottle.” A metal bellows is typically provided on one end of the bottle, and the movable contact is linked to the inside of the bellows. An operating rod attached to the outside of the bellows actuates the movable contact inside the bottle. The interior of the bottle is maintained under a controlled atmosphere, such as air under a low subatmospheric pressure, to protect the contacts from damage caused by arcing when the contacts are opened and closed. The glass or ceramic wall of the bottle provides a sealed enclosure, which maintains the controlled atmosphere for the life of the device. While efforts have been made to protect and reinforce contact assemblies with solid dielectric materials surrounding the bottles (as illustrated in the patents identified above), there is still a need for further improvements.
In particular, there is a significant, unmet need for an elastomer-insulated switch using a controlled atmosphere contact assembly, which would be suitable for underground power distribution systems and other, similar applications. Switches for use in these applications must meet several demanding requirements. The parts of the switch assembly connected to line voltage during use, including the contact assembly and operating rod, must be encased in a solid insulating housing. The housing must have dielectric strength sufficient to withstand the maximum voltage that may be imposed on the system, often as high as tens of thousands of volts for a distribution-level system. For safety, the insulating housing should be covered with a conductive layer that can be grounded. The switch should be operable from outside of the dielectric housing, without opening the housing and should be capable of withstanding many years of exposure to temperature extremes, water and environmental contaminants. The switch must also survive continued exposure to high voltages and withstand repeated operation. Most importantly, the switches must provide an easy and reliable indication of the position of the contacts.
Insulated switches using vacuum bottles do not provide means for visual inspection of the contacts to confirm that they are open (visible break) or closed. Prior art switches were designed with contacts in a large gas or oil filled cabinet which allowed a glass window to be installed for viewing the contacts. However, there is no means of directly viewing contacts in vacuum bottles since the bottles are made of metal and ceramic nontransparent materials. The seals required to maintain the vacuum inside the vacuum bottle prohibit the installation of a glass window. Newer high voltage switches combine vacuum switching with high dielectric strength EPDM rubber insulation as described in U.S. Pat. Nos. 5,667,060; 5,808,258; and 5,864,942 to Luzzi, all of which are incorporated herein in their entirety.
FIG. 1 shows a typical prior art insulated switch 900 using a vacuum bottle 902. The switch is sealed inside the vacuum bottle 902 and is hidden from view. The voltage source 904 and the load 906 are connected to the switch 900 but the switch contacts are not visible. The only means for determining the status of the switch contacts is the position of the switch handle 908. If the linkage between the handle 908 and the switch contacts is inoperative or defective, there is no positive indication that allows the operating personnel to determine the position of the contacts. Accordingly, the industry has recognized the need for insulated switches using vacuum bottles that provide a reliable indication of the position of the contacts.